Sensitive condition responsive control switch



y 4, 1942. J. E. LAKE 2,289,973

SENSITIVE CONDITION RESPONSIVE CONTROL SWITCH Filed July 22, 1941 2 Sheets-Sheet 1 Irwven'toP: John E.L ake,

W X WJW His Attormey- Patented July 14, 1942 SENSITIVE CONDITION RESPONSIVE CON- TBOL SWITCH I John E. Lake, Schenectady, N. Y., assignor to General Electric Company,

New York a l corporation of Application July 22, 1941, Serial No. 403,474

1': Claims. (01. 200-139) The invention relates to electric switches and particularly to sensitive, condition responsive control switches for use in condition control systems or other similar circuit control service.

One of the principal obiects'is to provide an improved sensitive control switch unit adapted for automatic operation by a sensitive, condition responsive device having a relatively feeble operating force.

Another object is to render the sensitive control switch unit capable or reliably controlling the maximum amount of electrical energy in both making and breaking the circuit with a minimum amount of mechanical energy input from the sensitive, condition responsive switch operating device throughout a maximum number of circuit controlling operations.

A further object is to provide improved means for varying the difl'erential of operation of the improved switch unit by the sensitive, condition responsive control device in closing and opening the circuit.

A still further object is to provide an improved form of sensitive temperature responsive operating mechanism for the switch.

More specific objects are to provide an improved anti-fraction, automatic wear compensating, current conducting pivotal mounting for the movable parts of the switch unit, an improved anti-welding switch contact magnetic field structure and an improved self-regulating, resilient snap action operating mechanism for eflectlng the closing of the switch contacts with a substantially constant contact closing pressure resiliently applied normally to the contacting surfaces so as to reduce the tendency for welding to occur at high values of current due to bouncing, sliding, or increase of. pressure between the contacts, and for separating the contacts with a slow motion, shorthammer blow that'is efl'ective both in interrupting high values of alternating currents and in breaking any slight welding or sticking of the contacts that may have occurred, Provision also is made for obtaining an increased force from the operating device for breaking the switch contactsapart in case the initial slow motion short hammer blow should fail to break any weld between the contacts.

Further objects and advantages of the present invention will become evident from'the following description of theaccompanying drawings illustrating preferred embodiments of the invention and in which Fig. 1 is a top view partly in section of an improved sensitive, thermostatically operated enclosed control switch with the enclosing cover removed; Fig. 2 is an end view from the left of the switch shown in Fig. 1 illustrating more clearly the improved switch differential regulating mechanism; Fig. 3 is a sectional view showing in detail the improved contact mounting and. snap action operating structure of the enclosed sensitive control switch unit; Fig. 4 is a top view of the switch structure shown in Fig. 3 with the enclosing cover removed; Fig. 5 is an enlarged view partly in section of one of the spring pressed current conducting mounting pivots of the switch shown in Figs. 3 and 4; Fig.

6 is a sectional view of a modified form of enclosed sensitive switch unit of the double contact type for opening one circuit and closing another circuit with a slow motion snap action;

and Fig. '7 is a top view ofthe double contact plate I2. bent over side, top, and bottom walls 2i, '22, and.

form of switch shown in Fig. 5 with. the enclosing cover removed.

In the improved thermostatic switch of Figs. 1 and 2, the sensitive control switch unit I0 is provided with a removable dust-tight cover Ilia, preferably of moulded insulating material, with a sliding operating pin Ii, also of insulating material, extending therethrough. The improved construction of the enclosed switch unit I0 is shown in detail in Figs. 3 and 4; The' switch unit In is mounted upon a bracket or plate 12 provided with suitably spaced holes for receiving the mounting bosses II and I5 projecting from the switch cover [0a with the operating pin ll mounted in a slide bearing formed centrally in the boss It so as to extend through the mounting plate l2. The switch unit it) is secured to the mounting bracket I2 by the mounting screws l6 and the bracket I2 is secured to a main base I 8 by the screws l9 which are threaded into the ears 2!) turned up from the edge of the The main base I8 is provided with metallic, sensitive temperature responsive operating element 30 is firmly secured, preferably by welding. The right-hand end of the adjusting shaft '21 is removably mounted in a bearing 3| formed in the end of the enclosing tube or dry well 32 which is sealed into a threaded mounting cap 34 so that the tube may be mounted in a tapped opening in the wall of a heating boiler, hot water tank, or any other fluid container and thereby render the sensitive thermostatic operating element 3|) responsive to changes in a predetermined temperature condition.

The base, |8 .is provided with a specially formed annular mountinghub 35 having a cylindrical portion 36 removably and adjustably mounted in the open end of the tube 32 with a groov 3'! in the outer' surface thereof for receiving the end of the holding screw 38. Upon loosening the screw 38, the entire switch mechanism may be readily adjusted into any desired angular position or removed from th tube 52 for inspection, repair, or replacement.

The left-hand end of the spiral thermostatic element 30 is secured. preferably by welding, to one leg of a substantially L-shaped switch operating lever Ml, the other leg of which is rotatably mounted by means of a single bearing ti upon the adjusting shaft 21 with the angularly bent arm 42 extending into operative relation with the switch operating pin II, as shown more clearly in Fig, 2. A switch differential regulating spring accepts a t operating lever it. The lever it is specially shaped at its ends and the two pivot pins 69 are specially located centrally of lever ill so that the pivot axis 69a extends substantially through the center of gravity of the switch operating lever i together with all the switch operating partscarried thereby. Thus the switch operating lever system is statically balanced in all operating po- 44 is secured at its left-hand end to the operating arm 42 with the right-hand end of the spring 44 biased into engagement with the traveling nut 45 mounted upon the differential adjusting screw 46 which is rotatably mounted in the yoke 5'! formed at the end of the arm 42. The improved manner in which the switch operating difierential adjustment is obtained is described hereinafter in connection with the operation of the thermostatic switch mechanism.

A temperature setting lever '50 is mounted on the adjusting shaft 21 by means of the mounting yoke 5| which carries a clamping screw 52 for tion on the shaft 21. An indicating pointer 53 on the lever extends through the arcuate slot 54 formed'in the upturned portion25 of plate i2 and cooperates with the calibrated temperature scale 55 that is adjustably mounted by means of th clamping screw 56 upon the outer face of the upturned portion 25 or the switch mounting plate i2, Thus angular adjustment of the shaft 21 by means of the lever 50 will vary the temperature at which the sensitive thermostatic element 30 operates the sensitive'switch Ill. The

clamping nut 58 holds shaft 21 in its adjusted angular position in socket 25 by cooperating with shoulder59. A

In the improved sensitive control switch'unit structure l0 illustrated in Figs. 3 and 4; the re-' movable enclosing cover Illa carrying the mounting bosses l4 and I5 and th switch operating pin H has a dust-tight peripheral engagement withv conical shape as shown in Fig. 5, for receiving in spring pressed pivotal current conducting relation therein a corresponding one of the rounded conically shaped mounting pins 69 extending from the opposite sides of the balanced switch the maximum amount of current to be conducted from the switch terminal strip 62 through the spring yoke 63. to the balanced switch operating securing the adjus ing lever 50in proper posishunts.

sitions independently of the particular position in which the switch it! may be mounted.

As shown in Fig. 5, the rounded conical dimples 58 are provided with a slightly wider internal angle than the external angle of the complementary rounded conical pivots 59 so as to obtain a narrow, annular, self-adjusting bearing andcurrent conducting contact therebetween closely encircling the pivot axis 690. as indicated by the dotted line C in Fig. 5. Moreover, these pivot angles and the opposing biasing forces exerted by the two arms 61 of the spring mounting yoke are so proportioned that both good current conducting contact pressure and automatic compensation for any slight wear occurring in the pivotal mounting are obtained. The resulting improved opposing spring biased pivotal switch self-adjusting,

mounting possesses yielding, shock-resisting characteristic that materially increase the operatinglii'e of the switch and also maintains the bearing friction that might interfere with the sensitivity and-accuracy of control- This improved spring at a minimum value. biased pivotal mounting arrangement permits member 10 without oven-heating and without the use of any flexible current conducting leads or The balanced switch operating lever I0 preterably is formed of magnetic material so that it can cooperate with a small permanent magnet N, preferably of sintered or cast form, to provide snap action operation of the switch. As shown, magnet" is mounted in attractive relationwith the left-hand end of the operating lever 10 mo recess 16- formed in the base 8| with its distance from and hence its magnetic pull on'the lever adjustable'by meansof the spring 15 and the adjusting screw I1. The snap action tilting movement of lever I0 towards and away from the magnet I4 is limited by means of the adjustable stops 80 and 8| which are threaded directly into the current conducting plate 62 and engage, re-

spectively, with theiower and'upper side of the right-hand end of the pivoted member 10. The stop 8| andthe pivoted operating member 10 preferably are silver plated so asto provide upon engagement thereof a good current conducting shunt path for diverting current from the pivot bearings 68 and 69 and thereby reducing the current heating efiect at the bearings, and increasing the effective life of the switch structure. Also the current conducting yok 6l preferably is silver plated so'that the plating in dimples '68 will cooperate with the plating on pivots 69 to provide a good current conducting wear resisting fiifvotal bearing thereby insuring a long operating The balanced operating lever I0 .carries the movable switch contact 83 that cooperates with the stationary switch contact as in opening and closing the circuit connected to the switch termlnals 66 and 9|, the latter being connected to stationary contact 84 .by rivet 92. The switch contacts operate in accordance with the present ining lever I8.

ventlon in a special relationship such that circuit making and breaking contact occurs therebetween substantially in the plane of the pivot axis 69a of the balanced operating lever 18 and relatively close to the axis with a substantially minimum relative movement between the contacts and a corresponding minimum tilting movement of the balanced operating lever I8. Also, both circuit making and breaking contact occurs substantially within the confines of a hole or aperture 85 provided in the magnetic material of lever 18 with the magnetic material closely surrounding the switch contacts. In addition, substantially a maximum constant preset pressure is resiliently applied to hold the movable contact 83 in circuit closing contact with the stationary contact 84 with the closing contact pressure applied in a direction that is substantially normal to the plane of the pivot axis 68a. Furthermore, the contact closing pressure is specially proportioned with removement of the contacts and a'corresponding this way the magnetic snap action of the switch operating lever 18 is regulated to produce rela tively slow motion of the movable contact 83 in both opening and closingthe circuit, as will be pointed out more fully in the following description of the switch operation.

Operation The improved sensitive thermostatic control switch shown in Figs. 1 and2 may be arranged to be responsive to the variations in any suitable temperature condition, and the switch terminals connected in any suitable control circuit. Howminimum tilting movement of the operating lever.

In the improved switch structure, the movable switch contact 83 is carried near the pivot axis 69a at one end of the resilient spring 86 which is secured at the other end thereof remote from the pivot axis to the bendable car 81 pressed out from the operating member I8. As shown more clearly in Fig. 4, the spring 86 is provided with a central looped portion 81 of substantially the same cross sectional area as the mounting portion 88 in order to allow the operating spring 83 to pass therethrough and still maintain a constant spring pressure gradient. However, the contact carrying end portion 89 of the spring is channel shaped so as to resist deformation, and a slight depression 38 is formed at the end of the spring 86 to provide a definite seat for the spring on the operatmaximum preset biasing force with which the end of the contact carrying spring 86 is biased into engagement with the balancedoperating lever 18 can be accurately proportioned so as to pro vide a substantially constant maximum contact closing pressure with a relatively low snap action force provided by magnet I4 as pointed out hereinafter. V

Tilting movement of the balance switch operating lever I8 is produced in both circuit opening and circuit closing operation by varying the force of the operating spring 83 which is interposed between the switch operating pin I I and the balanced switch operating lever I8. .The operating spring 93 extends through the looped portion 81 of the contact mounting spring 86 and is secured,

preferably by welding, at its end to an adjustable mounting ear 94 pressed out from the lever 78.

The force gradient of operating spring 83 is pro- Thus by bending the car 81, the f ever, the improved switch is particularly adapted to serve as a boiler aquastat to stop and start a burner motor in order to maintain the boiler water at a desired temperature, or as a limit switch to stop operation of the burner motor when the boiler water has reached a maximum safe temperature. But it will be evident that the improved thermostatically operated switch of the present invention is not necessarily limited to'such service but may be used wherever accurate and sensitive thermostatic control of a control circuit is desired. Also, it will be evident that the improved sensitive switch structure need not necessarily be operated by a sensitive temperature responsive device, but is equally advantageous in case the arm 42 is arranged to be operated by any other sensitive, condition responsive element having only a relatively feeble operating force such as a humidity responsive element, a pressure responsive element, sensitive electrical respcnsive element or the'like When the improved temperature responsive switch illustrated-is employed in boiler water temperature control service, any increase in temperature of the boiler water will be communicated through the tube 32 to the spiral thermostatic operating element 38. This element will warp so as to rotate the member 48 about the shaft 21 in the clockwise direction (Fig. 2) and thereby move the arm 42 towards the switch operating pin 'I I as the temperature increases. The difierential spring 44 will first engage with the rounded end of the pin II. But the force gradient of spring 44 is so proportioned that it is not strong enough to effect acircuit opening operation of the switch contacts 83 until the spring 44 has yielded and moved away from the adjustable stop 45 and into engagement with the arm 42 which serves as a fixed stop for limiting the maximum strain of spring 44. Thereupon the increased force exerted by the thermostatic element 38 is transmitted directly from the arm 42 through the spring 44 in its maximum strain limit position to the pin I I and thence through the spring 83 to the switch operating lever 18. When the force of spring 93 has been thus'increased sufficiently to slightly exceed the pull exerted by magnet 14 that holds lever 18 against stop 8|, then a slight accelerating force is available to start rotation of the balanced operating lever 18 about its pivot axis 69a.

With the lever I8 thus started in motion, it

hammer blow which ordinarily is sufficient to break any welding that may have occurredbetween the contacts 83 and 84. As the pivoted lever 18 moves away from -the magnet I4, the attractive pull therebetween inherently decreases at a rate determined by the adjustment of screw 11. As soon as the contact pressure spring 86 becomes seated on lever I8, it no longer exerts any force opposing the pull of the magnet. Since the accelerating rorcej of spring 88 is no longer rent can be successfully interrupted.

- example 4 or 5 mills;

added to that of spring 88, there is a sharp decrease in the spring force tending to-accelerate the contact opening movement of the pivoted slow switch openingmovement is of material advantage in interrupting the maximum amount of electrical energy in an alternating current control circuit; Due to the slow opening movement, the length of any arc drawn between the conassolovs Y lease ofthe strain of spring 44 the operating pin II can then travel along with'the'operating arm m.

42. In this way, the adjustment of nut 48 varies the temperature operating differential oi the switch. the stress in theswitch operating spring 88 has thus been relieved sufliciently so .-thatthe reduced pull oi the magnet I4 exceeds soon as the movable contact 88 engages the statacts 88 and 84 is held to .a minimum until the I alternating current passes through the zero value. Thereupon the cooling action 01' the contacts andethe surrounding metal parts of the operating member I8 at the edge of theopening 88 tends to condense any conductive vapors created by the arc so rapidly that arcingis not readily reestablished during. the succeeding" cycle of. the alternating current. The improved circuit interrupting action provided by thefiimproved switch structure of the present invention is so eii'ective that exceptionally high values 0! cur- The magnetic action set up in the magnetic material of lever 18 surrounding the hole or aperture 88 by the flow of relatively high currents through the switch contacts contributes to the eflectiveness of the circuit interrupting action.

' Since the current flowing in the contact pressure spring 88 is at right angles to the urrent flowing through the, contact 84 and rivet 82 to the terminal 8i, magnetic in terlal or the operating arm I8 is interposed betw resulting magneticii ds. This concentrates-the n and subject to both the strongestv magnetic field at the periphery of the hole 88 closely surrounding any are formed between the switch contacts 88 and 84. .But with the resulting magnetic fields at right angles there islittle if any tendency i'or the switch contacts to be separated by magnetic repulsion action when relatively,high values of current flow either in making or breaking the circuit.

Due to] the concentrated magnetic i ield and the rapid-vapor condensing action at the edge of switch contact closing pressure automatically balancing a substantial part thereof. This com- 'bination enables very sensitive and accurate control of a switch of relatively high current capacity to be obtained with a relatively i'eeble operating force. To eil'ect the operation of the switch from the open position to the closed position, the temtionary contact 84, the maximum preset biasing 'force of the contact pressurespring '88 atonce ll rebound or chattering. Since the maximum becomes eflective' to resiliently hold contact 88 in engagement with contact v84 so as to prevent preset biasing force-oi. spring 88 is applied norahd the'iace of stationary contact 84, there' is no tendency for contact 88 to slide uponcontact 84. This materially reduces the chances ior any appreciable welding to occur inclosing the switch contacts with high inrush current values such as are likely to occur in inductive alternating current circuits. Also this helps to maintain the operating differential oi the switch relatively constant. a As the switch contacts close, the increasing pull of magnet I4 on-lever I8 is opposed by both the preset biasing force'oi spring 88 and also the increasing stress built up in spring 88. As a re- "sult, the continued pivotal movement or the Upon closing the switch, the engagement oi Q the right-handend oi operating member 10 with the head of the stop screw 81 establishes a good conducting path in shunt with the pivot bearings for diverting a substantial part of the current in the circuit controlled by the switch from the bearings. Thus the pivot bearings carry the to-' ts] current only momentarily.

In case any substantial welding of the switch cient to break the contacts-apart. In this case,

continued movement of the arm 42 will continue movement 01' the operating pin II to increase perature to which the thermostatic element 88 is a responsive must decrease. Thereupon, the operating arm 42 is moved away from the switch operating pin ll. But the diflerential regulating spring 44 still exerts a large enough force upon the pin II to maintain spring 88 stressed sumciently to oppose the reduced pull of magnet" that holds the "switch operating lever I8 against the strain set up in spring 88. Finally, as the spring 88 bends, the finger 88 carried thereby is brought into engagement with the end oi'the pivotedlever III. In this way the force 01' the operating arm 42 is transmitted directly through" the pin it and the finger 88 to the end 01' the pivoted lever Ill, thereby providing an increased force tending to break the switch contacts 88 and 84 apart. 'The strengthening channel section 88 formed at'the end of the contact pressure spring 88 transmits the increased force from the lever 18 to the contact .88.

In the modified form structure shown in Fig. 6, the switch is of the double throw type adapted to break one. circuit and make another circuit. The general features-of construction of the enclosing casin the magnet mounting and adlusting mechanism, and also the improved spring biased pivot mounting shown in Fig. 5 for the movable switch parts are substantially the same as'those described in connection with the single throw switch of Figs. 8 and 4. However, with.

described.

the double throw switch, the special current conducting spring yoke 63 is mounted centrally oi the switch base Gla so as to receive the pair or mounting pivot pins 69 that extend centrally from the opposite sides of the balanced pivoted switch operating lever 10a. The permanent magnets I4 and 14a are mounted in magnetic attractive relation' with the opposite ends of the lever 10a. A contact pressure spring IIII has one end thereof secured, preferably by welding, to the slotted ear HIi at the end of the pivoted lever 70a which may be bent so that the contact I02 is carried at the other end of spring IOI in a hole or aperture I03 formed in the lever 10a with a preset contact closing pressure in cooperating circuit controlling relation with the sta-- tionary contact I04 to which the switch terminal I05 is connected. Similarly, the contact pressure spring I06 is adjustably secured at the opposite end of the lever a and carries the movable contact I01 in the opening I08 formed in lever 0 in cooperating circuit controlling relation with the stationary contact I 09 to which the switch terminal H0 is connected.

The pivoted lever 100. carries centrally thereof the mounting rivet III to which the bow spring H2 is secured at substantially its center, preferably by welding, with one end of the bow spring H2 in operative relation with the operating pin II and the other end in operative relation with the adjusting screw H3.

As shown, the operating pin I I has been depressed so as to set up a strain in the right-hand end of the spring H2 sufllcient to tilt the pivoted lever 10a out of attractive relation with the left-hand magnet I4 and into attractive relation with the right-hand magnet 14a, and at the same time set up a strain in the left-hand part of the bow spring H2 suflicient to return the pivoted lever 10a, to its initial position when the force operating the pin II is removed. During the tilting movement of the lever 10a, contact I02 is separated from the contact I04 with a short hammer blow in substantially the same manner as described in the separation of the contacts of the switch of Figs. 3 and 4 to obtain high current interrupting ability with a minicircuit and operated by the sensitive thermostatic element 30 of Figs. 1 and 2 or by other suitable condition responsive means.

The tilting movement of the pivoted switch lever 10a is limited by the adjustable screw stops I I8 and I I9, the former limiting the tilting movement towards the left-hand magnet I4 and the latter limiting the tilting movement towards the right-hand magnet 14a. The stop H8 is threaded into the specially formed conducting plate I22 which is connected by the conducting rivet I23 with the central switch terminal and also is connected by the rivet I25 with the spring pivot, yoke 03. Thus a good conducting shunt around the spring pivot bearings is established movably mounted on said lever and having preset contact closing pressure means, spring pivot means for mounting said lever and conducting current through said lever to said movable contact, a stationary contact cooperating with said I movable contact to control a circuit, a current conducting stop for said lever connected in said circuit in shunt with said spring p'ivot means upon operation of said lever to close said circuit,

mum movement of the switch operating pin I I.

Likewise, during the final tilting movement of the pivoted lever 10a, the contact IN is brought into engagement with the contact I00 in substantially the same manner described in connection with the switch in Figs. 3 and 4 without rebounding, chattering or liability of welding of the switch contacts for exactly the same reasons as previously pointed out.

Upon the release of the operating force impressed upon the operating pin II, the strain set up in the left-hand part of bow spring H2 becomes effective to return the pivoted member 100. to its initial biased position. In the initial part of this return tilting movement of lever 10a, the contact I 01 is separated from the stationary contact I08 with a short hammer blow and continued slow motion to provide the high current circuit interrupting capacity previously Subsequently the contacts I02 and I04 are engaged in the manner described.

The double throw switch shown in Figs. 6 and 7 is provided with three terminal connecting screws H5, H6, and II I which are connected respectively to the spring pivot yoke 63, the'stationary switch contact I04 and the stationary switch contact I09. Thus the switch may be employed in the ordinary form of 3-wire control variable spring means for biasing said lever to operate said movable, contact from the circuit closing position to the circuit opening position, magnetic means for variably opposing the combined biasing action of said spring means and saidcontact closing pressure means to efiect a regulated snap action movement of said lever in operating said movable contact each way be tween said circuit controlling positions and for biasing said lever to operate said movable contact to the circuit closing position, temperature responsive means having a movable operating member for varying said spring biasing means to efiect operation of said lever, and an auxiliary spring biasing means movable with said operating member and interposed between said member and said spring biasing means and provided with an adjustable stop carried by said operating member for regulating the operating temperature difierential of said lever.

2. In combination,a movable current conducting switch member having spring pivot current conducting mounting means and a current conducting stop in shunt therewith, variable spring means for biasing said member away from said .stop, magnetic biasing means for variably opposing the biasing action of said spring means to effect snap action movement of said switch memmagnetic means for biasing said member from one circuit controlling position to another cir- I cuit controlling position, variable spring biasing meansfor variably opposing the biasing action of said magnetic means to effect snap action movement of said switch member each way bea movable member and an auxiliary biasing spring mounted on said member for varying said variable spring biasing means and provided with a fixed stop for limiting the maximum strain of. said auxiliary biasing spring and adjustable stop for limiting the release of said strain to regulate the operating diiferential'of said switch member.

4. In combination, a movable switch member, variable biasing means for biasing said member from one circuit controlling position to another circuit controlling position, cooperating biasing means for variably opposing the biasing action of said first biasing means to effect snap action movement of said switch member each way between said circuit controlling positions and for biasing said member to said other circuit controlling position upon apredetermined variation of said first biasing means, and condition responsive means having a'movable member and an auxiliary biasing spring mounted on said member for varying said first biasing means and provided with a fixed stop for limiting the maximum strain of said auxiliary biasing spring and an adjustable stop for limiting. the release of said strain to regulate the operating differential of said switch member.

5. In combination, a snap action switch biased to one circuit controlling position, and condition responsive means having a movable member and an auxiliary biasing spring mounted on said member for operating said switch to another circuit controlling position and provided with a fixed stop for limiting the'maximum strain of said auxiliarybiasing spring and an adjustable stop for limiting the release of said strain to regulate the operating differential of said switch.

6. A thermostatic switch comprising in combination, a snap action switch biased-to one circuit controlling position, a mounting bracket therefor provided with annular mounting means for varying the angular position of said bracket, a tube closed at one end and having means at the open end thereof for mounting said tube in a wall and for supporting said annular mounting means in axial alignment with said tube, a shaft extending axially-through said annular mounting means with one end thereof rotatably mount- .ed in said closed end of said tube and having adjustable mounting means for securing said shaft to said bracket in different angular positions, a substantially L-shaped switch operating lever having one legrotatably mounted on said shaft and provided with a biasing spring having an adjustable stop for regulating the operating differential of said switch unit with the other leg extending through said annular mounting one end of said shaft and the other end thereof lar positions with said opening in alignment with said tube, a shaft extending through said opening switch in accordance with variations in the tem- I perature of said element.

8. In combination, a switch having annular mounting means, a shaft extending axially through said annularmounting means, a substantially L-shaped switch operating lever having one leg thereof rotatably mounted on said shaft with the other leg extending through said annular mounting means, and a spiral bimetallic operating element having one end secured to saidv shaft and the other end secured to said lever.

9. In a switch, in combination, a substantially. balanced magnetic operating lever sides thereof with an opening in said lever adjacent the pivot axis and provided with a bend-.-

ableear remote from said axis, a contact closing pressure spring having a switch contact at one end thereof and the other end thereof secured to said bendable ear for movably supporting said contact in said opening with said spring biased to provide a preset contact closing pressure normal to the plane through said axis and l the face of said contact, a current'conducting spring yoke provided with a complementary rounded conical shaped dimple in each arm thereof for receiving in spring pressed pivotal current conducting relation therein a corresponding one of said pivots, a stationaryswitch contact cooperating with said'movable contact to make and break a circuit in said plane, a

magnet in attractive relation with one end of said lever for biasing said lever to operate said movable contact to the circuit closing position, an operating spring cooperating with said preset contact closing pressure spring for variably opposing the biasing action of said magnet to effect a regulated snap action movement of said lever in opening and closing the circuit and for biasing said lever to operate said movable contact to the circuit opening position, and a current conducting stop for engaging the other end of said lever to shunt said current conducting pivots upon snap action operation of said lever to close said contacts.

10.- Ina switch, in combination, a switch operating lever having opposite,rounded conical pivots, a movable switch contact mounted on said lever, a current conducting spring yoke provided with a complementary rounded conical shaped dimple in each arm thereof for receiving in spring pressed pivotal current conducting relation therein a corresponding one of said pivots, a stationary switch contact cooperating with said movable contact to control a circuit, and a v current conducting stop for engaging said lever to shunt said current conducting pivots upon operation of said lever to close said contacts.

11. In a switch, in combination, a switchopcrating lever having opposite "mounting pivots, a

having rounded conical pivots extending from opposite switch contact mounted on said lever, a current conducting spring yoke provided with a complementary dimple in each arm thereof for receiving in spring pressed pivotal current conducting relation therein a corresponding one of said pivots, a stationary switch contact cooperating with said movable contact to control a circuit, means for effecting snap action pivotal movement of said lever in opening and closing the circuit, and a current conducting stop for engaging said lever to shunt said current conducting pivots upon snap action operation of said lever to close said contacts. 12. In a switch, in combination, a magnetic switch operating lever having opposite pivotal mounting means and an opening in said lever adjacent the pivot axis, a switch contact having means for mounting said contact on said lever in said opening with a preset contact closing pressure, a current conducting spring yoke provided with complementary pivotal mounting means in the arms thereof for establishing spring pressed pivotal current conducting relation with said opposite pivotal mounting means, a stationary switch contact cooperating with said movable contact in said opening to provide a magnetic field in making and breaking a circuit, opposing biasing means for effecting a regulated snap action movement of said lever in opening and closing the circuit, and a current conducting stop for engaging said lever to shunt said current conducting pivotal mounting means upon operation of said lever to close said circuit.

13. In a switch, in combination, a switch operating lever, a movable switch contact resiliently mounted on said lever, spring pivot means for mounting said lever and conducting current through said lever to said movable switch contact, a stationary switch contact cooperating with said movable contact to control a circuit, and a current conducting stop for said lever connected in shunt with said spring pivot means upon operation of said lever to close said circuit.

14. In a switch, in combination, a substantially balanced pivoted operating lever, a movable switch contact, a spring for mounting said,

contact on said lever to provide a preset contact closing pressure normal to a plane through the pivot axis and the face of said contact, a stationary switch contact cooperating with said movable contact to make and break a circuit in said plane, and biasingmeans for efiecting a slow motion hammer blow of said lever on said spring in opening the circuit.

15. In a switch, in combination, a substantially balanced pivoted magnetic operating lever having an opening therein, a switch-contact movably mounted on said lever in said opening and having biasing means for providing a preset contact closing pressure normal to a plane through the pivot axis and the face of said contact, a stationary switch contact cooperating with said movable contact to make and break a circuit in said plane, and snap action means including a magnet and an opposing spring cooperating with said contact biasingmeans to effeet a slow motion hammer blow of said lever on said movable contact in breaking the circuit.

16. In combination, a control member movable between two control positions, a variable biasing means for biasing said member to move from one of said positions to the other, an opposing ,variable biasing means effective upon predominance thereof over said first biasing means for biasing said member to move from said other position to said one position, and condition responsive means having a pair of relatively movable operating members movable as a unit upon response of said condition responsive means to variation of the condition to one value for varying said second biasing means into predominance over said first biasing means and having relative movement therebetween upon response of said condition responsive means to opposite variation of the condition to another value for oppositely varying said second biasing means out of predominance over said first biasing means, and provided with an adjustable stop for controlling the relative movement between said members to determine said other value.

17. In combination, a control member movable- .between two control positions, opposing variable biasing means therefor, and condition responsive means having a pair of relatively movable operating members movable as a unit for varying one of said biasing means into predominance over the other and thereby biasing one position.

JOHN E. LAKE. 

